The present invention relates to ultrasonic flow measurement systems and particularly to wedges or buffer rods used to couple a transducer to a pipe or conduit wall for effecting a fluid measurement.
In general it may be said that accurate ultrasonic flow measurements require that the paths of interrogation, whether along diameter paths of a conduit or chordal paths such as those used in quadrature systems, be well defined in order to accurately apply equations to compute flow. In clamp-on systems in the prior art this has often entailed mounting wedges axially centered on a conduit or effecting precision machined bores in the conduit to receive special waveguides. Well defined paths are especially important for off-diameter paths lying outside the mid-radius circle, where the flow profile is sharply curved. Such paths have generally been achieved with precision bores holding straight waveguides. Indeed, it would appear a contradiction of objectives if one sought to obtain well defined paths using refracted beams of ultrasound.
Applicant has previously proposed a measurement system wherein vertically polarized shear waves were used to measure flow. The system involved a buffer rod having a half inch square cross section in which vertically polarized shear waves were transmitted to the pipe. Another buffer rod construction is shown in U.S. Pat. No. 3,973,152 issued to Karplus. That construction utilizes a large number of sheets which are pressed together to make a wedge. This design does not specifically deal with the notion of interposing a long buffer or long heat dissipating member between a hot pipe and a piezo transducer which must remain cool. Rather, in proposing a laminated construction, the '152 patent aims to reduce ringing that occurs in solid wedge designs. Another buffer rod construction appears in applicant's earlier U.S. Pat. No. 3,575,050, issued Apr. 13, 1971. Various other designs are known either for wedges which allow a transducer to be clamped onto a pipe without special machining, or for buffer rods which allow a transducer to connect to a hot pipe without heating excessively. However, the very traits which make a buffer rod a good waveguide may also result in ringing, or restrict the buffer to a limited number of frequencies or wavetypes, or result in a poorly directed output beam. Similarly, mounting wedges generally require specific set-up, or are configured for one size or range of pipe, and generally launch refracted waves through the wall along a diametral path.
Thus there remains a need for more versatile and effective coupling for ultrasonic transducers, and especially for a buffered coupling or waveguide which is adaptable to various pipe orientations to launch signals with a high degree of accuracy and control.